Cathode structure



Nov. 21, 1961 H. J. DAILEY ETAL 3,010,046

CATHODE STRUCTURE Filed Feb. 26, 1952 Fig. I

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wmwzsszs; INVENTORS Hampton J. Bailey and R'odger G. Larson.

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United States 3,010,046 CATHODE STRUCTURE Hampton J. Dailey, Verona, and Rodger G. Larson, East Orange, N.J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 26, 1952, Scr. No. 273,386 6 Claims. (Cl. 313-346) Our invention relates to electron discharge tubes, and more particularly to a cathode for such tubes.

In accordance with the prior art, of which we are aware, cathode structures have been built comprising a closed structure having a porous tungsten wall in one end of the structure. Inside the structure there is a barium-strontium carbonate reservoir. This cathode is satisfactory for some purposes. However, for many purposes the high temperature required during activation and the migration of barium to nearby structures, has been found to cause it to be undesirable.

The emission mechanism of this structure has been ascribed to the diffusion of barium through the tungsten wall when the barium carbonate was converted to barium oxide and reduced by the tungsten.

It is accordingly an object of our invention to provide an improved cathode for use in another electron discharge device.

Another object of our invention is to provide a cathode which does not contain materials which require chemical reduction or outgassing.

Another object of our invention is to provide a cathode having means for producing a high degree of control of the temperatures involved.

Still another object of our invention is to provide a cathode having a reservoir containing barium which may be readily reactivated after exposure to air.

An ancillary object of our invention is to provide a new and useful electronic apparatus.

The novel features which we consider characteristic of our invention are set forth with more particularity in the appended claims. The invention, however, with respect to both the organization and the operation thereof, together with other objects and advantages may be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIGURE 1 is a cross sectional showing of a cathode embodying our invention,

FIG. 2 is a schematic showing of a cathode in accordance with our invention inside a cathode-ray tube.

In accordance with our invention, we provide an outer cylindrical wall 4 of electrically conducting material such as molybdenum. Inside the outer cylindrical wall there is a cylindrical cup-shaped box 6, the outside dimensions of which near the open end 8 of the cup 6 are substantially equal to the inside dimensions of the outer cylindrical wall 4. At the end of the cup opposite the open end, the cup walls extend inward so as to form a smaller cylindrical cavity 10 which has one open end 12, opening into the main part of the cup-shaped box 6.

Across the open end 8 of the cup-shaped box 6 there is a sintered porous tungsten plug 14 which completely fills the open end 8 of the cup 6. On the outer side of the tungsten plug 14 that plug has a concave surface 16 for providing focusing of electrons emitted from the Patented Nov. 21, 1961 tungsten wall. In the small cavity 10 at the bottom of the cup 6, there is a barium slug 18 with a coating 20 of a protecting metal preferably nickel thereon. Welds 22 are provided between the barium slug 18 and the wall of the small cavity 10, for maintaining the slug 13 in a fixed position.

Primary heating coils 23 encircle the small cavity 10 at the bottom of the cup 6 for heating the nickel coated barium 18-, 20 so as to cause evaporation of the barium. Outside the outer cylindrical wall 4 opposite the porous tungsten plug 14, there may be a secondary heating coil 24 for controlling the temperature of the tungsten plug 14. The tungsten plug 14, the wall of the inner cup 6 and the outer cylindrical wall 4 are preferably welded together.

The present apparatus has the advantage that no materials are present which require chemical reduction or outgassing as was required previously in cathodes of this type. By employing two separate heating coils, one in the region of the tungsten plug and the other in the region of the barium, it is possible to control the temperature of the emitting surface and the temperature of the barium reservoir independently of each other when desired. Such a control allows a material lengthening of the life of the cathode.

By controlling the rate of evaporation of the barium which may be achieved by controlling the rate of evolution from the slug and by using the getter action of the barium, it is relatively easy to reactivate the cathode after exposure to air.

In FIGURE 2 we have shown a cathode-ray tube cornprising an evacuated envelope 26 having therein an anode 2.8 and a cathode 30 of the type shown in FIG. 1 and described above.

While we have shown this cathode in a cathode-ray tube, it is nevertheless understood that it may be used in many other types of tubes. For example, the resistance of this cathode to back bombardment is excellent, therefore, it should be exceptionally useful in magnetrons and other electron tubes.

Although we have shown and described specific embodiments of our invention, we are aware that other modifications thereof are possible. Our invention, therefore is not to be restricted except insofar as is necessitated by the prior art and the spirit of the invention.

We claim as our invention:

1. A cathode comprising a molybdenum tube having therein a nickel coated barium slug which is surrounded by a heater coil, a wall of molybdenum across said tube on one side of said barium, and a wall of porous tungsten across said tube on the other side of said barium.

2. A cathode structure comprising, a supporting tube across said tube on the other side of said barium, and a heater coil in the region of said tungsten wall for heating said wall.

4. A cathode structure comprising, a supporting tube of heat resistant material having an open end, a piece of 4 r 6. A cathode comprising a nickel coated barium slug enclosed in a chamber, said chamber having part of its I walls composed of a porous metal, and a heating element near said chamber for heating said siug. 5 References Cited in the file of this patent UNITED STATES PATENTS 'Espe June 21, 193s Lemmens et a1. Feb. 27, 1951 

1. A CATHODE COMPRISING A MOLYBDENUM TUBE HAVING THEREIN A NICKEL COATED BARIUM SLUG WHICH IS SURROUNDED BY A HEATER COIL, A WALL OF MOLYBDENUM ACROSS SAID TUBE ON ONE SIDE OF SAID BARIUM, AND A WALL OF POROUS TUNGSTEN ACROSS SAID TUBE ON THE OTHER SIDE OF SAID BARIUM. 